MONDAY, March 2, 2015 (HealthDay News) -- Acetaminophen may not be as safe as previously thought, with larger doses and long-term use linked to increased risk of health problems, a new report contends.

Best known in the United States under the brand name Tylenol, acetaminophen is the most widely used painkiller in the world, the study authors said in background notes.

It is the World Health Organization's front-line treatment for pain, and is considered safer than nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen, the researchers said.

But a small group of studies has raised questions about acetaminophen's safety if used for a long time and at high doses to treat chronic pain, said lead author Dr. Philip Conaghan, a professor with the Leeds Institute of Rheumatic and Musculoskeletal Medicine in England.

Heavy use of acetaminophen is associated with kidney disease and bleeding in the digestive tract, the paper reports. The medication also has been linked to increased risk of heart attack, stroke and high blood pressure, the study authors noted.

One cited study even showed that overuse of acetaminophen can increase a person's risk of early death as much as 60 percent, the study authors found.

"Bigger doses seem to be more associated with those side effects," Conaghan said. "It's yet another reason for us to be careful of what drugs people take long-term, because they all have side effects."

The study authors are calling for a new systematic review of acetaminophen's effectiveness and safety, saying that the medication's true risks are "higher than that currently perceived in the clinical community." The cited side effects appear similar to those of NSAIDs.

Acetaminophen still seems safe when taken occasionally, or when taken at moderate doses for treatment of long-term chronic pain, said Dr. Robert Wergin, president of the American Academy of Family Physicians.

"It still may be the right drug, if used at the proper dose," Wergin said. "I feel like this study probably wouldn't change my message to my patients," which includes telling them to avoid extra-strength versions of acetaminophen and stick to the directions for use.

Still, Wergin said, the new paper "shows that acetaminophen is not a benign drug. You still have to pay attention to dosage."

The paper's authors reviewed 1,888 studies related to the use of acetaminophen. They settled on eight studies that met the standards for their review. The studies involved more than 665,000 people in the United States, Britain, Denmark and Sweden.

"McNeil Consumer Healthcare is committed to providing consumers with safe and effective over-the-counter medicines and recommends consumers always read and follow the product label," a statement from the company reads. "If consumers have questions regarding the products they are taking, we encourage them to contact their doctor or pharmacist."

Because the studies were observational, they don't prove a cause-and-effect relationship between acetaminophen and these health problems.

Dr. Nortin Hadler, emeritus professor of medicine at the University of North Carolina at Chapel Hill, said people might take more acetaminophen as a result of the health problems being blamed on the drug.

"Chronic kidney disease includes a fair amount of aches and pains," Hadler said. "Maybe it's the cart and the horse. They took acetaminophen because they had chronic kidney disease. They didn't develop chronic kidney disease because they took acetaminophen."

Other painkillers and medications taken also might have contributed to the health problems observed in these studies, the paper's authors noted.

The studies tracked patients from as few as two years up to as many as 20, Conaghan said.

The studies also differed in how patients' acetaminophen use was calculated, Conaghan said. Some studies estimated lifetime intake, while others reported the amount taken each day, week or month -- making it impossible to draw firm conclusions about what constitutes a "safe" dose.

Conaghan said he'd like to see people focus more on lifestyle changes that have been proven to aid pain management -- strength training, physical activity and weight loss, among them.

"The problem is, all of those things are not as easy as taking a pill, and so they aren't as attractive to people," he said.

The paper was published online March 2 in the journal Annals of the Rheumatic Diseases.